A highly selective magnetic sensor with functionalized Fe/Fe3O4 nanoparticles for detection of Pb2+

A magnetic sensor for detection of Pb²⁺ has been developed based on Fe/Fe₃O₄ nanoparticles modified by 3-(3,4-dihydroxyphenyl)propionic acid (DHCA). The carboxyl groups of DHCA have a strong affinity to coordination behavior of Pb²⁺ thus inducing the transformation of Fe/Fe₃O₄ nanoparticles from a dispersed to an aggregated state with a corresponding decrease, then increase in transverse relaxation time (T2) of the surrounding water protons. Upon addition of the different concentrations of Pb²⁺ to an aq. solution of DHCA functionalized Fe/Fe₃O₄ nanoparticles (DHCA-Fe/Fe₃O₄ NPs) (Fe] = 90 mmol/L), the change of T2 values display a good linear relationship with the concentration of Pb²⁺ from 40 mmol/L to 100 mmol/L and from 130 mmol/L to 200 mmol/L, respectively. Owing to the especially strong interaction between DHCA and Pb²⁺, DHCA-Fe/Fe₃O₄ NPs exhibited a high selectivity over other metal ions.